The present invention relates to a positive-working, radiation- or photosensitive composition comprising, as the essential constituents,
(A) a polymeric binder which is insoluble in water and soluble in aqueous-alkaline solutions; and
(B) a 1,2-quinonediazide or a combination of
1. a compound which, under the action of actinic radiation, forms a strong acid and
2. a compound which possesses at least one cleavable C--O--C bond, the solubility of which in a liquid developer is increased by the action of acid, and to a radiation-sensitive recording material comprising a support coated with a layer of said composition and suitable for the production of printing plates and photoresists.
Positive-working photosensitive compositions, i.e. compositions which comprise the above-mentioned constituents and the photosensitive layers of which are rendered soluble in the exposed areas, are known.
The vast majority of these compositions contain phenol/formaldehyde condensation products, particularly novolaks, as alkali-soluble binders. Other alkali-soluble binders which can be used and which are described in the art, include homo- and copolymers of vinyl phenol, copolymers of maleic acid anhydride and styrene, copolymers of vinyl acetate and crotonic acid, copolymers of methyl methacrylate and methacrylic acid, or novolaks which have been modified by chloroacetic acid. However, these binders have been unable to gain general acceptance. Virtually all commercial products which are known, therefore, contain novolaks. Novolaks used as binders, however, have disadvantages for particular applications.
A fundamental drawback of the novolaks resides in their insufficient thermal stability. If, for example, dry plasma etching is employed in the production of integrated circuits by means of photoresist processes, the photoresist used must stand the high temperatures occurring in the process without any deformation or other change of the image. The novolaks customarily employed do not, however, meet this requirement. As the softening range of the novolaks is between 120.degree. C. and 130.degree. C., the resists start to flow when these temperatures are exceeded. As a consequence thereof, the structures get blurred, which results in a poor resolution.
A similar disadvantage of the novolaks is observed when they are used as binders in positive printing plates.
For increasing the print run the printing plates are baked for some minutes at temperatures of about 200.degree. C. to 250.degree. C. after development. During this stage, parts of the novolak and other layer constituents may escape from the layer and redeposit on the bared aluminum surface, which in the printing process leads to scumming, i.e., to an undesired ink acceptance of nonimage areas.
If positive layers are employed in dry resist processes, the layers must be soft and flexible to ensure an unobjectionable processing. In the subsequent electroplating step, the softness of the layer may cause problems, due to, for example, diffusion of low molecular weight layer constituents from the layer and undercutting of resist edges.
There have been proposed a number of ways to overcome these disadvantages.
In U.S. Pat. No. 4,439,516, o-quinonediazides are combined with polyvinylphenols. It is true that due to the high softening range (above 150.degree. C.) of the employed polyvinylphenol, the photoresists obtained are capable of standing elevated temperatures without any deformation of the image, but at the same time this parameter has a disadvantageous effect on the mechanical properties of photoresist layers of this type. These resists cannot be processed as dry resists in the form of rolls, since in these processes, a thermoplastic flow at about 100.degree. C.-130.degree. C. is required for lamination to a substrate. Furthermore, layers containing these substances are very brittle and have a tendency to splinter when being cut.
U.S. Pat. No. 4,456,679 has disclosed a positive-working mixture which in addition to the photosensitive o-nitrocarbinol ester groups contains crosslinking compounds which, under the action of heat, react with the carboxyl groups present following exposure, whereby a covalent bond is formed. The disadvantages of this process reside in the known low photosensitivity of the o-nitrocarbinol esters and in that, after imagewise exposure and development, a second overall exposure is necessary for the thermal crosslinking of the resist layer.
Furthermore, German Offenlegungsschrift No. 32 46 037 and U.S. Pat. No. 4,387,152 describe low-molecular weight compounds possessing methylol groups, methylolether groups, or methylolester groups capable of crosslinking, which are used as additives in mixtures of o-quinonediazides and novolaks and, at elevated temperatures, effect thermal crosslinking with the novolak and thus lead to higher print runs. In the baking step or in electroplating baths these additives can, however, escape from the layer and cause problems.
In the prior, not prepublished German Offenlegungsschrift No. 33 29 443, there has been disclosed a photopolymerizable mixture comprising ethylenically unsaturated polymerizable compounds, customary binders and photoinitiators, as well as a binder with thermally crosslinkable side groups of the formula --CH.sub.2 OR, with R denoting hydrogen, an alkyl group, an acyl group or a hydroxyalkyl group.